The floors of the buildings or houses usually comprise a subfloor or foundation commonly made of unfinished wood or concrete, and a top floor having a visible upper finished surface. The top floor may consist of one or more layers of wood, resilient tile or sheet, ceramic tile, carpet, linoleum, etc.
It is known in the art that an intermediate layer (also called "underlayer") can be inserted between the subfloor and the top floor so as to provide resiliency and sound absorbing properties to the same. These layers are commonly manufactured as substrates that can be laid and secured onto the subfloor. In this connection reference can be made to the following U.S. patents, which disclose underlayers consisting of a uniform layer of cellular foam or rubber.
U.S. Pat. No. 2,811,906 (Chappel)
U.S. Pat. No. 3,579,941 (Tibbals)
U.S. Pat. No. 4,112,176 (Baileys)
U.S. Pat. No. 5,016,413 (Counihan)
Other documents, such as, for examples, U.S. Pat. No. 4,109,041 (Tellman) and the defensive publication U.S. T931,006 (Akron), suggest that the rubber may come from recycled used tires.
U.S. Pat. No. 4,759,164 relates to a flooring structure which comprises an underlayer made of a resilient material. The bottom surface of this underlayer is provided with spaced-out channels of a substantially U-shaped cross-section (see FIGS. 4 to 6 of it). The channels are spaced apart from one another and used as a venting system. Because of these channels, only a portion of the overall bottom surface of the underlayer is in contact with the subfloor. However, this portion represents more than 75% of the overall bottom surface.
As can be easily understood, it is desirable for the substrates used as underlayers in a flooring structure to be manufacturable at a given cost while showing good sound absorbing properties.
It is also desirable that such substrates be provided with good acoustic insulation properties while having a minimum thickness.